Communication system



March 9, 1943.

G. VALENSI COMMUNICATION SYSTEM Filed Nov. 17; 1959 5 Sheet s-Sheet 1hat Qn QM a Q I March 9,1943. G, VA ENS, 2,313,209

' COMMUNICATION SYSTEM Filed Nov. 17, 1939 5 Sheets-Sheet 5'EDIIEIIIIUIII March 9, 1-943. VALENSI I 2,313,209

I COMMUNICATIAON SYSTEM Fiied Nov. 17, 1939 5 Sheets-Sheet 4 -llllllllllifijill lllllI' II- WMMNWMMM Patented ar. 9, 1943 ooimuumca'no vSYSTEM Georges Valensi, Parl Q, France; vested iii-the Alien PropertyCustodian Application November 17, 1939, In France November Serial No.304,884 a. 1938 Y 3 Claims. (Cl. 178-50) The invention relates"- toimprovements in or relating to communication systems and moreparticularly to telegraphy and telephony, and has for one of its objectsa multiple transmission of messages over a given link without increasingthe frequency band needed. Another object is to reduce the frequencyband. Yet another object is to provide secrecy of transmission.

The present invention is based on the fact that for manytelecommunication purposes and particularly for telegraphy andtelephony, it is not necessary to reproduce at the receiving end of atransmission link the amplitudes of the currents with extreme precision.Even for telephony it will be sufficient to discriminate between a'limited number of amplitude levels (say 6 or If we assume that the linkbetween the sending and receiving stations is able to transmitfaithfully the amplitude variations in much greater detail than requiredto transmit the limited number of levels of one telephone channel, itmay be considered possible to use the link to pass the necessaryinformation to obtain a second telephone channel without increasing thefrequency range.

A given amplitude of the line current may be considered as representingacertain combination of the instantaneous amplitudes of the twotelephone channels, in accordance with a certain code. A system based onthe above principle will therefore include a coding arrangement at. thesending ,end and a decoding arrangement at the receiving end.

For telegraphy only two amplitude levels may be considered assatisfactory and the property of the link of transmitting faithfullymuch smaller variations in level may therefore be used to pass theinformation needed by several other telegraphic channels.

According to the present invention the respective simultaneoustransmissions of intelligence are diflerentiated from one another, notaccording to frequency as in known multiplex communication systems, butaccording to amplitude, the respective channels having differentamplitude ranges. A device herein termed a coding device is used at thetransmitting station for 4 convertingthe instantaneous amplitudes of thesignal wave forms transmitted over the respective input channels topredetermined levels and for combining the latter into a single codedsignal" for transmission over a line or other transmission medium. Atthe distant receiving station, a device herein termed a. decodingdevice" responds to the coded signal and derives from it the originalinstantaneous amplitudes of the signal wave forms which arethenimpressed upon the respective output channels.

Theabove principle will be better understood by referring to the figuresattached, of which:

Fig. 1 represents a typical arrangement enabling to send three telegraphmessages through a single link.

Fig. 1A represents another arrangement of the sending part of Fig. 1.

Fig. 2 represents a typical terminal equipment to obtain two both-waytelephone channels over a single link. r

Figs. 3a, 3b, 30 represent resistance arrangements which can be used inthe coding apparatus.

Fig. 4 indicates the'principle of using a cathode-ray tube withfluorescent screen, code screen and photo cell.

Fig. 5 represents a typical decoding arrangement.

Fig. 6 represents a complete schematic of a terminal equipment for twoboth-way telephone channels.

In Fig. 1 the parts indicated by M1 M1 M1 M1 represent a quadrupletelegraph key (for example the 4 armatures of a transmitting relay whichare mechanically, but not electrically, connected together)corresponding to the first telegraph channel. The parts Mal M22represent a double telegraph key corresponding to the'second telegraphchannel and M: a simple telegraph key corresponding to a third telegraphchannel.

To each part of the keys (M for instance) corresponds a back (orspacing) position (In: for example) and a front (or marking) position(b'ia for example). The stops of the quadruple key of the lst channel inwhich the level differ= ences are small, are electrically connected totappings of a current supply apparatus (for examconnected to the doublekey of the 2nd channel,

,so that for this 3rd channel the level-variations are again greater. Itis understood that in operation the keys for each of the channels mustbe in one of the marking or spacing positions and not in an intermediateposition. 4

The following table indicates for each combi- Qnation of the signals ofthe 3 channels, the value of the E. M. F. acting on the link LI andproduced by the coding arrangement COD.

E. M. F. acting Signal in the Signal in the Signal in the on the link(in first telegraph second telet ird televolts) channel graph channelgraph channel emitting cathodes m, 72, we,

The same result can be obtained by the arrangement of'Fig. 1A, on whichare shown the keys MiMzMs corresponding to the 3 telegraph channels andsources of current of variable E. M. F. (for example 10, 20, 40' v.)

This figure shows more clearly that, in the above case, the line signalsare the addition of the signals of the various channels.

At the receiving end (Fig. l) the decoding arrangement DEC consists forexample in three cathode ray switches C1, C2, C3, having electronandaccelerating anodes which are not shown. The deflector plates (61 51' 6262' 6a 63') are connected (through polarising batteries 91 Pa 2 3) tothe resistances, r1, r2, n, which are in parallel with the line L1. Thepotentials between the deflector plates are the same for the 3 tubes andthe deflections are proportional to the variations of the E. M. F. atthe sending end.

The resistances 11, T2, 13 and the batteries 171, pa, pa are adjusted insuch a way that the electron beams touch on! in C1, the lower part of(12 in C2 and the lower part of (13 in C3 when the E. M. F. operating onthe line is 0. When the E. M. F. has its full value ('70 v.) thecontacts a1", (12 (upper part) and m (upper part) are touched. I

The plates a1 er" of the cathode switch C1 are connected to two points51, p1 of the current supply P1 which is connected to the cathode '71through the winding of the receiving telegraph relay of the firstchannel. The plates as er are connected to the points 52, ,92' of thesource Pa which is connected to the cathode '72 through the telegraphrelay of the second channel. The plates 3 and as are connected to thepoints 53, p3 of the source Pa, connected to the cathode '73 through therelay R3 of the third channel. As the distance between successive platesat (in C1 C2, C3) is supposed to be negligible in comparison with thewidth of these plates, the electron beams scan .these plates in such away that the receiving telegraph relays R1, Ra, Ra take the requiredspacing and marking positions in accordance with the following table:

M1, M1 M1 are on their spacing contacts, M2 M2 are on their markingcontacts and M2 is on its spacing contact. Across line I, a voltage of20 volts is applied from point 20 on the resistance across P, biz, M1,1721, M, be, Ma, 11, 1'2 and rain parallel to 0. The cathode rays 0! thetubes will be deflected ihto contact with C1 to on (spacing), C2 to 0:2lower half (marking) and C: to as near center (spacing). Movement of anyone of the keys to a different position, for example, M3 to marking,will apply 60 volts across'the line, applying spacing potential in C1 aton, marking potential in C2 at 0:2 and marking potential in C: at ora Itis understood that the transit time of any of the keys is shorter thanthe marking or spacing period.

It will be seen that the receiving relays take the positionscorresponding to those required by the coding table.

The code used contains 2X2 2 combinations as there are 2 positions foreach of the 3 channels. With n channels having 91 levels for the firstchannel pi levels for the second and 1211 levels for the nth. channel,the code would have p1 p2 pn combinations.

In case of telephony some 6 to 10 levels may be needed and if Weconsider 2 channels, we would need 6 6=36 to 10 10=100 combinations. Theintervals between the levels of one of the channels would be 6 to 10times the intervals between the levels of the other channels. Thesignals of one channel would be added to the signals of the otherchannel at the sending end and at the receiving end the signals can bereceived by using two cathode ray tubes in an arrangement similar tothat of Fig. 1. As the telephone channels must operate in bothdirections, an arrangement imilar to that of Fig. 2 can be used.

This figure represents the terminal equipment needed to enable twosubscribers to communicate over their lines A and B with theircorrespondents over the common line L'. The usual hybrid coils TA, TB,TL, and balancing networks BA, BB, B1. are used in such a waythat speechcoming from Decoding table t t e r ph channel 2nd telegraph channel 3rdtelegraph channel 11 11111 in volts E M F acting out e e( toifcggii g gfioi figgg Pgs ign ft figi g in P323105? 0 Spacingi Spacing.-. agspacing a} Marking-- a2 -do Spacing-u Marking 3 30 g" a}, do ,,3 40 iSpacing-h .a, Spacing, Marking. Marking" a; do 80 i Spacing-4 a: MarkingDo. Marking. Do.

While the .above description clearly points out the operation of thesystem an explanation of the conditions presented in the present showingof Figure 1 may further simplify an understanding of the system. Asshown,

armatures M1 A and B is directed respectively throu h plifiers AA and Asto the coding arran ge i e ig The coded signals are then directedthrough Tr. to the line L. Signals arriving from the line are directedthrough the amplifier Ar. to the desistances r1 r1 opaque compartmentsbetween the tube and cell coding arrangement and from here respectivelyto the lines A and B.

It is understood that the transmission equivalent of the line should bekept constantwithin certain limits and that this may be done eventuallyby using a pilot frequency and automatic regulation. Repeater ga'ins maybe kept constant by using negative feed-back.

We may now consider more closely the coding arrangement.

In the simplest case the telephone currents would be amplified in such away that the maximum level of one channel is, say fitimes greater thanthat oi the other, and the two currents would be added together. meansof a three-winding transformer or by passing each current through aresistance (or a reactance) connecting these resistances in series andtaking the total potential difference as input of an amplifier forexample.

Instead of such a simple network, the current of one or both channelsmay go first to a vacuum tube and the addition of the currents orpotentials be made afterwards.

The coding arrangements may aim use a kind of cathode ray tube, theelectron beam (of circular or rectangular cross section) beingcontrolled electrostatically or electro magnetically by the speechcurrents.

The electrons may reach conducting electrodes brought out of the tubeand connected to difierent potentials as shown in Fig. 1 or-connected todifferent resistances in series with a given E. M. F. These resistanceswill be of an order of magnitude equal to the resistance of the electronbeam. When resistances are used, they may be placed inside the tube sothat only one wire need be brought out. The resistance may in this caseconsist of a resistant layer deposited on an insulator in one continuoustrain as shown in Fig. 3a or in'several ones 1; 1'2 fn connectedtogether by good conductors as shown in Fig. 3b.

- 'In these cases the electron beam when directed at a certain moment tosome point of this layer insert in the circuit a certain length of thelayer. The current variations would be gradual, at least when theelectron beam is deflected in one direction.

The variable current may also be obtained by providing a series ofsquare or rectangular conducting plates connected together through re-1-11 1-11 asshown in Fig. 3c. The distances between the plates would besmall compared to their dimensions if square signals are wanted.Refinements using auxiliary plates and resistances or an electron beamof relatively large section could be provided if the signals have to beshaped in some special way The resistances between the plates may allhave the same values or have different values, some plates may bestrapped together, etc., depending on the particular code used.

Another method of obtaining the current variations would be to producesecondary emission on the spot touched by the electrons. The intensityof this secondary emission would vary from point to point either due tothe nature of the surface touched, to variable electric or magneticconditions, or to the use of screens.

The coding arrangement may also use a cathode ray tube C withfluorescent screen Fl, the light of which, concentrated by an opticalsystem L, acts on a photocell Ph as shown by Fig. 4. The variations ofphotocell current could then be obtained by inserting a code screen Swith This can be done'by escent material and on the other side witha'moreor less opaque layer producingthe required variations in the lighttransmitted to the photocell.

Regarding the. decoding solutions, similar to those of the codingarrangement, may be considered.

The signals have to be split into their constituent parts. This may bedone by extracting individually all the parts from the line current or(particularly inthe case of two telephone channels) by extracting firstthe signals of the channel using large variations in level and thensubtracting these from the total line currents. An example of been givenin Fig. 1 for the case of telegraphy. Fig. 5 gives an example of theother procedure.

accelerated by the anode 28-a to. which is applied a certain potentialby the D. C, supply 2l a. pending on the instantaneous value of thedeflecting current the electron beam will reach one of the conductingplates Cl, Ca. C6,.C7 fixed in the tube. These plates are connected tothe high tension supply 33-a through resistances R1, R2 Rs, R1, and acommon current in the resistance lid-a'wili vary by steps when the beampasses next one. The resistances will be calculated in such a way that,if the current is I when the beam reaches C1, the current will be 21, 31II, when reaching C2, C3 C1 respectively.

It will be seen that in this way it is possible to obtain in theresistance 3fia the current values of one of the telephone channels. Bysubtracting the potential between the terminals of 34-4 resistances 32band 33b of the plate circuits of the vacuum tubes 30!; and 3lb inopposition. The apparatus 24b can be adjusted in sucha. way that therequired gain (or attenuation) is obtained. 1

The Fig. 5 shows vacuum tubes, but a similar result could be obtained bysending the cathode ray tube currents through a resistance connected inseries with another resistance through which passes a currentproportional to the total line current in the required phase relation sothat the diiierence between line current and cathode ray tube currentmay be obtained for reproducing the second speech channel, as explainedfurther in relation with Fig. 6.

We may now consider thecomplete schematic of Fig. 6 showing a preferredarrangement of the terminal equipment used for two both-way telephonechannels. In this figure, two subscriber lines may be connected to thejacks A and B and the subscribers should be able to communicate1vivithLtheir correspondents through the common arrangement several thefirst procedure has already I beam sweeps over The currents from A aredirected by means of the hybrid coil TA through a high pass filter FA(which eliminates the frequencies below 300 c./s., which are noteffectively transmitted by the line) to the amplifier AA which isprovided with an automatic volume control arrangement" and then to thedeflecting coil 1 of the coding cathode ray tube M. A source of E. M. F.Pa is provided'to have unidirectional deflections of the electron beam.

The currents from B follow a similar path and reach the coil 2 whichproduces a deflection at right angles with that-of coil I. The electronan assembly of plates and resistances as illustrated by Fig. 3c andproduces current variations which are amplified by A3. The levels arecompressed by the arrangement C and then sent to the line L through thehybrid coil T1,. The use of this compresser avoids too low levels on theline and consequently possible distortion of signals due to noise,crosstalk and interference.

The currents coming from the line L pass to the expander E whichrestores the correct levels, then to the amplifier A4 and to the coil 3of the decoding cathode ray tube N. An F. Pa is provided to restore theD. C. componen The cathode ray tube N contains as many plates andresistances as there are levels in channel A so that the current flowingthrough the resistance R1 reproduces the level variations of thischannel. These variations reproduce the speech current, a low passfilter FA eliminating the components above 2400 c./s. the requiredoutput level to the speech currents which pass through the hybrid coilT. and to the line A.

The resistance R1 is connected in series with the resistance R throughwhich passes a current proportional to the incoming currents. Thedifference of the potentials at the terminals of R1 and R gives thelevel variations of the channel B and these signals, after passingthrough the :low pass filter F's and the amplifier A's are sent throughthe hybrid coil TB to the line B. r

In the preceding cases no attempt has been made to reduce the frequencyband which has to be transmitted over the line. The purpose was totransmit several messages without needing more than the total frequencyband available. It may however be interesting in certain cases Anamplifier A's gives to transmit only one message, but to reduce thefrequency band. Supposing speech over a line passing only frequenciesfrom 300 to 1300 c. /s.: it the original speech band containsfrequencies from 300 to 2300, this band could be split into two part bymeans of filters we want to transmit and the highest part (1300 to 2300)be transposed by suitable modulation to the range 300- 1300. The twoparts can then be considered as two messages to be transmitted togetherover the line as in the preceding cases.

At the receiving end, one of the parts would be replaced in its initialfrequency position and be added to the other part to reconstitute theoriginal speech.

The resent invention gives a certain secrecy, as a mere listening on theline would only enable to understand parts of the conversations, mainlyof the channel using high levels.

This secrecy may be increased by using codes in whichthe line currentsare not merely the sum of the individual channel currents, but in whicha certain line amplitude would represent any combination of channelamplitudes. This would be particularly easy when cathode ray tubes andphoto-electric cells are used.

In case of a single telephone channel, the line signals could becompletely distorted by providing a second channel carrying only adisturbing noise. At the receiving end, the separation would be done inthe same way as channels. The noise could be charged from time to timeif required. In case of telegraphy, several telegraph channels could bemixed with one noise channel.

I wish it to be known that I do not desire to be limited to the exactdetails of construction shown and described, for obvious modificationswill occur to persons skilled in the art.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a two-way two-channel telephone channel, for each channel a hybridcoil, a balancing network and a coding system for replacing the originalvoice-frequency wave by a series of finite amplitude levels according tothe amplitude of the wave, and a decoding system for separating incomingsuperposed amplitude levels, and means for connecting said coding anddecoding devices to the multiplex transmission line comprising a hybridcoil and the balancing network.

2. In a transmission system in which the signals are analysed in afinite series of amplitude levels, means for effecting suchtransformation comprising a cathode ray tube, means controlled by signalcurrents for deflecting the cathode rays of said tubes, and multipleanodes connected to series resistances of approximately same magnitudeas electron beam resistances, placed inside or outside the cathode raytube.

3. A multiplex telecommunication system in which a plurality ofintelligence channels are provided over the same transmission medium,comprising a plurality of independent signs. sources, one for eachchannel, means to transmit signal currents from each of said sources atdifierent amplitude levels, the range of amplitude levels beingdifferent for each channel, a coding device for combining signalcurrents from said sources into a common coded signal current having anamplitude varying according to th sum of the instantaneous amplitudes ofthe wave forms of the signal currents from said sources, means fortransmitting said coded signal currents over the transmission medium toa receivcathode ray of said tube, and multiple anodes connectedto seriesresistances of approximately the same magnitude as the resistance of theelectron beam, said resistances being located inside the cathode raytube.

- GEORGES VALENSI.

for two telephone

